Compressors and pistons for use in such compressors

ABSTRACT

A piston for use in a compressor comprises a head portion and an engaging portion. The engaging portion includes a first shoe pocket and a second shoe pocket formed therein, and an interior surface of the first shoe pocket includes a hollow potion formed therein. Moreover, the interior surface of the first shoe pocket includes a lubrication layer formed thereon. For example, the lubricant layer may include a solid lubricant or a grease having a viscosity which is sufficient to adhere the grease to the interior surface of the first shoe pocket or the second shoe pocket, or both. In an embodiment, an interior surface of the second shoe pocket also may have the hollow portion formed therein. In another embodiment, the interior surface of the second shoe pocket may have a penetrating aperture formed therein.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to compressors for use in automotive air conditioning systems, and pistons for use in such compressors. In particular, the invention is directed towards compressors and pistons, in which sufficient lubrication is provided between a shoe and a shoe pocket which receives the shoe.

[0003] 2. Description of Related Art

[0004] Known swash plate-type compressors include a housing, a swash plate, a plurality of pistons, and a plurality of shoes which each piston engages the swash plate. The housing comprises a crank chamber and a plurality of cylinder bores formed therethrough. The swash plate is rotated by a rotation of a drive shaft which is driven by a driving force, e.g., an engine of a vehicle. Each piston is positioned within a corresponding one of the cylinder bores and reciprocates within the corresponding cylinder bore to compress a refrigerant. Each piston includes a cylindrical, head portion, and the head portion comprises an engaging portion which extends from an end therefrom. A pair of shoe pockets are formed opposite each other within the engaging portion of the pistons. Each of the plurality of shoes are positioned within a corresponding shoe pocket, such that each shoe is positioned between the corresponding shoe pocket and the swash plate. Each shoe is in sliding contact with an end surface of the swash plate. Moreover each shoe pocket comprises a concave, hemispherical cross-sectional shape, and a convex, hemispherical portion of each shoe is positioned within the shoe pocket. When the swash plate rotates, portion of each shoe slidably contacts the swash plate and the shoe pocket.

[0005] When the refrigerant is compressed by the piston, a compressive force is applied to those portions of the shoe and the shoe pocket, which contact each other. In such known compressors, a difference between a diameter of the shoe pocket and a diameter of the hemispherical portion of the shoe is selected, such that lubricating oil suspended in the refrigerant is introduced between those portions of the shoe and the shoe pocket, which contact each other. Moreover, a surface of the shoe pocket is roughened to introduce the lubricating oil between these portions of the shoe and the shoe pocket, which contact each other.

[0006] In another known swash plate-type compressor, such as the compressor described in U.S. Pat. No. 5,784,950, the disclosure of which is incorporated herein by reference in its entirety, a communication hole is formed through a portion of the shoe pocket, and a recess is formed in an interior surface of the shoe pocket. The recess is machined by a leading end of a drill, which is used to form the communication hole, and the recess retains lubricating oil. Moreover, the lubricating oil retained by the recess and blow-by gas supplied at the start of compressor operation may lubricate those portions of the shoe and the shoe pocket, which contact each other.

[0007] Nevertheless, if a vehicle using such known compressors is not used for a extended amount of time, e.g., several months, the refrigerant may condense and accumulate in a crank chamber of the compressor, or the refrigerant may evaporate. Moreover, the condensed refrigerant may wash away the lubricating oil which adheres to sliding components of such known compressors, e.g., the shoes, the pistons, the swash plate, or the like, or the lubricating oil separates from the refrigerant, which reduces the amount of lubricating oil between the sliding components of the compressors. When the vehicle has not been used for the extended amount of time and the compressor begins to operate, friction between those portions of the shoe and the shoe pocket, which contact each other may become excessive, which may result in galling or scoring of the shoe pocket. Moreover the compressor may seize shortly thereafter, e.g., within two seconds after commencement of compressor operation.

[0008] While not willing to be bound by a theory, it is believed that scoring or galling, or both, may occur because the coefficient of friction between those portions of the shoe and the shoe pocket, which contact each of exceed a maximum coefficient of friction. Moreover, when compressor operation begins, friction between the sliding components of the compressor may remain excessive until the sliding components adapt to each other. Specifically, in swash plate-type, fixed displacement compressors, the angle of a swash plate does not vary. When the pistons approach a top dead center position or a bottom dead center position, the area of the shoe which contacts the shoe pocket is at a minimum. Consequently, when a reactive force from a compression chamber is applied to the shoe and the shoe pocket, the compressor may seize. Moreover, in compressors using single headed pistons, the piston at a side of the shoe and at a side of the head piston is less balanced relative to if double headed pistons are used. Therefore, the piston and the shoe may seize when they receive a force other than the reaction force.

[0009] In known compressors, such as the compressor described in U.S. Pat. No. 5,784,950, although most portions of the shoe and the shoe pocket, which are in sliding contact with each other, are sealed, some of these portions are not sealed. Consequently, when the compressor has not been used for the extended amount of time, the refrigerant may wash away the lubricating oil retained in the recess formed in the interior surface of the shoe pocket. Moreover, if liquefied refrigerant accumulates in the crank chamber, lubricating oil included in the blow-by gas provided to the shoe pocket via the communication hole may not reach the shoe pocket for a period time greater than about two (2) seconds after compressor operation begins. Therefore the compressor may seize shortly after compressor operation begins, e.g., within about two (2) seconds of the commencement of compressor operation.

SUMMARY OF THE INVENTION

[0010] Therefore, a need has arisen for a swash plate-type compressor which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that sufficient lubrication is provided between those portions of the shoe and the shoe pocket, which contact each other, such that the incidence of compressor seizure when compressor operation commences is reduced.

[0011] In an embodiment of the present invention, a compressor for use in an automotive air conditioning system comprises a front housing and a cylinder block comprising at least one cylinder bore formed therethrough. The compressor also comprises a drive shaft rotatably supported by the cylinder block and the front housing, and a swash plate rotatably mounted on the drive shaft. Moreover, the compressor comprises at least one piston positioned within the at least one cylinder bore. The at least one piston comprises a head portion and an engaging portion. The engaging portion comprises a first shoe pocket and a second shoe pocket formed therein, and an interior surface of the first shoe pocket comprises a hollow portion formed therein. The interior surface of the first shoe pocket also comprises a lubricant layer formed thereon. Moreover, the compressor comprises at least one first shoe positioned between the swash plate and the first shoe pocket, and at least one second shoe positioned between the swash plate and the second shoe pocket.

[0012] In another embodiment of the present invention, a piston for use in a compressor comprises a head portion and an engaging portion. The engaging portion comprises a first shoe pocket and a second shoe pocket formed therein, and an interior surface of the first shoe pocket comprises a hollow portion formed therein. The interior surface of the first shoe pocket also comprises a lubricant layer formed thereon.

[0013] In still another embodiment of the present invention, a piston for use in a compressor comprises a head portion and an engaging portion. The engaging portion comprises a first shoe pocket and a second shoe pocket formed therein, and an interior surface of the first shoe pocket comprises a hollow portion formed therein. The interior surface of the first shoe pocket also comprises a lubricant layer formed thereon, and an interior surface of the second shoe pocket comprises a penetrating aperture formed therein.

[0014] In yet another embodiment of the present invention, a method for manufacturing a piston comprising a head portion and an engaging portion comprises the step of forming a first shoe pocket and a second shoe pocket within the engaging portion. The method also comprises the step of forming a hollow portion within an interior surface of the first shoe pocket, and coating the interior surface of the first shoe pocket with a lubricant.

[0015] Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a more complete understanding of the present invention, the needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings.

[0017]FIG. 1 is a longitudinal, cross-sectional view of a swash plate-type, fixed displacement compressor, according to an embodiment of the present invention.

[0018]FIG. 2a is a side view showing an engaging portion of a piston, according to an embodiment of the present invention.

[0019]FIG. 2b is an enlarged, cross-sectional view of a shoe pocket of the piston at a side of a cylinder bore, which has a solid lubrication layer, according to the embodiment of FIG. 2a.

[0020]FIG. 2c is an enlarged, cross-sectional view of a shoe pocket of the piston at a side of the cylinder bore, which has a liquid lubrication layer, according to the embodiment of FIG. 2a.

[0021]FIG. 2d is an enlarged, cross-sectional view of the shoe pocket at aside of a crank chamber, according to the embodiment of FIG. 2a.

[0022]FIG. 3a is a side view showing a method of manufacturing the piston of FIGS. 2a-2 c.

[0023]FIG. 3b is an enlarged, cross-sectional view of the shoe pocket at the side of the cylinder bore, according to the embodiment of FIG. 2a.

[0024]FIG. 4a is a side view of an engaging portion of a piston, according to another embodiment of the present invention.

[0025]FIG. 4b is an enlarged, cross-sectional view of the shoe pocket at the side of the crank chamber, which has the solid lubrication layer, according to the embodiment of FIG. 4a.

[0026]FIG. 4c is an enlarged, cross-sectional view of the shoe pocket at the side of the crank chamber, which has the liquid lubrication layer, according to the embodiment of FIG. 4a.

[0027]FIG. 5a is a side view showing a method of manufacturing the piston depicted in FIGS. 4a and 4 b.

[0028]FIG. 5b is an enlarged, cross-sectional view of the shoe pocket of the piston at a side of a cylinder bore showing the method of manufacturing the piston of FIGS. 4a and 4 b.

[0029]FIG. 6 is a longitudinal, cross-sectional view of a swash plate-type, variable displacement compressor, according to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] Preferred embodiments of the present invention and their features and advantages may be understood by referring to FIGS. 1-6, like numerals, being used for like corresponding parts in the various drawings.

[0031] Referring, to FIGS. 1-3 b, a compressor 100 for use in an automotive air conditioning system according to an embodiment of the present invention is shown. Referring specifically to FIG. 1, a swash plate-type, fixed displacement compressor, 100 may comprise a front housing 18, a cylinder block 13, a valve plate 24, and a cylinder head 23 which may be fixed to each other by a plurality of bolts 50. A plurality of cylinder bores 12 may be formed in cylinder block 13, and cylinder bores 12 may be arranged radically with respect to a center axis of cylinder block 13. Compressor 100 also may comprise a drive shaft 19, a swash plate 14, a plurality of pistons 16, and a plurality of shoe pairs 15 a and 15 b. Swash plate 14 may be mounted on drive shaft 19 and may maintain its angle against an end surface 11 of cylinder block 13. Each piston 16 e.g., a single headed piston, may be positioned within a corresponding one of cylinder bores 12, such that each piston 16 reciprocates independently within the corresponding one of cylinder bores 12. Each piston 16 may be connected to swash plate 14 via a corresponding one of shoe pairs 15 a and 15 b. In compressor 100, swash plate 14 may be positioned within a crank chamber 17 and crank chamber 17 may be formed by front housing 18 and cylinder block 13. Drive shaft 19 may extend along a center axis of compressor 100 through crank chamber 17, and drive shaft 19 may be rotatably supported by front housing 19 and cylinder block 13.

[0032] In operation, when a driving source, e.g., an engine of a vehicle, rotates drive shaft 19, swash plate 14 also rotates. The rotational movement of swash plate 14 may be converted into a linear reciprocating movement which may be transmitted to piston 16. Consequently, piston 16 reciprocates within cylinder bore 12. When piston 16 reciprocates within cylinder bore 12, refrigerant is drawn into cylinder bore 12 from a suction chamber 21, and piston 16 compresses the refrigerant. The compressed refrigerant subsequently is discharged into a discharge chamber 22.

[0033] Piston 46 may comprise a head portion 25 and an engaging portion 26. Head portion 25 may be positioned within cylinder bore 12, and engaging portion 26 may positioned within crank chamber 17. Referring to FIG. 2a, a hollow chamber 32 may be formed within head portion 25, and a recess 27 may be formed at engaging portion 26. A pair of shoe pockets 28 a and 28 b may be formed within a first side wall and a second wall of recess 27, respectively, and shoe pockets 28 a and 28 b may hold shoes 15 a and 15 b, respectively. Each shoe 15 a and 15 b may comprise a convex, hemispherical portion and a substantially flat portion. Each shoe pocket 28 a and 28 b may comprise a concave, hemispherical portion to receive the convex, hemispherical portion of shoes 15 a and 15 b, respectively. Each shoe 15 a and 15 b may be positioned slidably within a corresponding one of shoe pockets 28 a and 28 b, respectively.

[0034] Referring to FIGS. 1-2 d, shoe pocket 28 a may be positioned at a side of cylinder bore 12, and shoe pocket 28 b may be positioned at a side of crank chamber 17. A hollow portion 31 may be formed at a center of shoe pocket 28 a. Hollow portion 31 may comprise a cylindrical portion and a cone portion, and hollow portion 31 may not extend through hollow chamber 32 For example, the diameter of the cylindrical portion of hollow portion 31 may be less than or equal to about three (3) mm. Moreover, a penetrating aperture 33 may be formed through shoe pocket 28 b which may be positioned opposite hollow portion 31. For example, the diameter of penetrating aperture 33 may be less than or equal to about three (3) mm. In another embodiment, hollow portion 31 may be formed at a center of shoe pocket 28 b, and penetrating aperture 33 may be formed through, shoe pocket 28 a.

[0035] Referring to FIGS. 3a and 3 b, hollow portion 31 and penetrating aperture 33 may be formed using a drill 34. Specifically, penetrating aperture 33 may be formed by drill 34, and subsequently, hollow portion 31 may be formed by drill 34.

[0036] Moreover, an interior surface of at least one of shoe pockets 28 a and 28 b may be coated by a lubricant to form a lubrication layer 29 on the interior surface of at least one of shoe pockets 28 a and 28 b. For example, referring to FIG. 2b, in an embodiment, lubricant layer 29 may comprise at least one solid lubricant, e.g., molybdenum disulfide, graphite, tungsten disulfide, poly-tetra-fluoro-ethylene, tin, stannum, or the like. Referring to FIG. 2c, in another embodiment, lubricant layer 29 may comprise a liquid lubricant, e.g., grease having a viscosity which is efficient for the grease to adhere to the interior surface of shoe pockets 28 a or 28 b, or both. For example, the grease may have a National Lubricating Grease Institute (“NLGI”) consistency grade of 9. Referring again to FIGS. 2a-2 d, in an embodiment, the interior surface of shoe pocket 28 a and shoe pocket 28 b may be lubricated with the lubricant to form lubricant layer 29 on the interior surface of shoe pocket 28 a and the interior surface of shoe pocket 28 b. Subsequently, compressor 100 may be manufactured, and then hollow portion 31 may be sealed by the hemispherical portion of shoe 15 a. Therefore, even if lubricating oil in crank chamber 17 is washed away, e.g., when the vehicle is not used for the extended amount of time, lubricant layer 29 is not readily washed away. Consequently, when compressor operation commences, a sliding portion between the interior surface of shoe pocket 28 a and the hemispherical surface of shoe 15 a is sufficiently lubricated, and compressor 100 may not seize. Moreover, during operation, hollow portion 3l may retain the lubricating oil, e.g., when the lubricant layer 29 comprises the liquid lubricant, as shown in FIG. 2c. Therefore, the sliding portion between the interior surface of shoe pocket 28 a and shoe 15 a remains sufficiently lubricated even if lubricant layer 29 washes away from the interior surface of shoe pocket 28 a or shoe pocket 28 b, or both. Further, once shoe pocket 28 b and shoe 15 b adapt to each other, lubricating oil comprised in blow-by gas readily may enter the sliding portion between the interior surface of shoe pocket 28 b and the hemispherical surface of shoe 15 b via penetrating aperture 33.

[0037] Referring to FIGS. 1 and 4a-5 b, a compressor 100 for use in an automotive air conditioning system according to another embodiment of the present invention is shown. The features and advantages of this embodiment of the present invention are similar to the features and advantages of the above-described embodiments of the present invention. Therefore, the features and advantages of the above-described embodiments of the present invention are not discussed further with respect to this embodiment of the present invention. In this embodiment, a first hollow portion 35 may be formed at a center of shoe pocket 28 b, and a second hollow portion 31 may be formed at a center of shoe pocket 28 a, such that first hollow portion 35 may be positioned opposite second hollow portion 31. Moreover, an interior surface of at least one of shoe pockets 28 a and 28 b may be coated by the lubricant to form lubrication layer 29, as set forth with respect to the above described embodiments of the present invention.

[0038] Referring to FIGS. 5a and 5 b, a method for forming first hollow portion 35 and second hollow portion 31 is shown. Hollow portions 31 and 35 may be formed using a ball end mill 36. Ball end mill 36 may cut the surfaces of shoe pockets 28 a and 2 b, thereby forming hollow portions 31 and 35. In another embodiment, hollow portions 31 and 35 may be formed by forging. Moreover, an interior surface of at least one of shoe pocket 28 a and shoe pocket 28 b may be coated by the lubricant used in the above-described embodiments of the present invention. For example, shoe pocket 28 a and shoe pocket 28 b may be coated with the lubricant. Subsequently, compressor 100 may be manufactured, and then hollow portions 31 and 35 may be sealed by the hemispherical surfaces of shoes 15 a and 15 b.

[0039] Referring to FIG. 6, the above-described embodiments of the present invention also may be use in a swash plate-type, variable displacement compressor 100′. The features and advantages of this embodiment of the present invention are similar to the features and advantages of the above-described embodiments of the present invention. Therefore, the features and advantages of the above-described embodiments of the present invention are not discussed further with respect to this embodiment of the present invention. In compressor 100′, a rotor 37 may be fixedly connected to a drive shaft 19, and swash plate 14 may be slidably mounted on drive shaft 19. Swash plate 14 may be connected to rotor 37 via a hinge mechanism 38, such that an inclination angle of swash plate 14 may vary and swash plate 14 rotates with drive shaft 19. During operation of compressor 100′, the inclination angle of smash plate 14 is controlled by a capacity control mechanism 39, and the inclination angle of swash plate 14 varies.

[0040] While the invention has been described in connection with preferred embodiments, it will be understood by those skilled in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are consider exemplary only, with the true scope of the invention indicated by the following claims. 

What is claimed is:
 1. A compressor for use in an automotive air conditioning system comprising: a front housing a cylinder block comprising at least one cylinder bore formed therethrough; a drive shaft rotatably supported by the cylinder block and the front housing; a swash plate rotatably mounted on the drive shaft; at least one piston positioned within the at least one cylinder bore, wherein the at least one piston comprises: a head portion; and an engaging portion comprising a first shoe pocket and a second shoe pocket formed therein,, wherein an interior surface of the first shoe pocket comprises: a hollow portion formed therein; and a lubrication layer formed thereon; at least one first shoe positioned between the swash plate and the first shoe pocket; and at least one second shoe positioned between the swash plate and the second shoe pocket.
 2. The compressor of claim 1 wherein the lubrication layer comprises a solid lubricant.
 3. The compressor of claim 1 wherein the lubrication layer comprises a grease having a viscosity which is sufficient to adhere the grease to the interior surface of the first shoe pocket.
 4. The compressor of claim 1, wherein an interior surface of the second shoe pocket is coated with the lubricant.
 5. The compressor of claim 1, wherein the first shoe comprises a flat portion and a hemispherical portion, and the hemispherical portion of the first shoe is positioned within the first shoe pocket, such that the hollow portion is sealed by the first shoe.
 6. A piston for use in a compressor comprising: a head portion; and an engaging portion comprising a first shoe pocket and a second shoe pocket formed therein, wherein an interior surface of the first shoe pocket comprises: a hollow portion formed therein; and a lubrication layer formed thereon.
 7. The piston of claim 6, wherein the lubrication layer comprises a solid lubricant.
 8. The piston of claim 6, wherein the lubrication layer comprises a grease, and the grease has a viscosity sufficient to adhere the grease to the interior surface of the first shoe pocket.
 9. The piston of claim 6, wherein an interior surface of the second shoe pocket comprises the lubrication layer, formed thereon.
 10. The piston of claim 9, wherein the interior surface of each of the first shoe pocket and the second shoe pocket comprises the hollow portion formed therein.
 11. A piston for use in a compressor comprising: a head portion; and an engaging portion comprising a first shoe pocket and a second shoe pocket formed therein, wherein an interior surface of the first shoe pocket comprises: a hollow portion formed therein; and a lubrication layer formed thereon, wherein an interior surface of the second shoe pocket comprises a penetrating aperture formed there.
 12. The piston of claim 11, wherein the lubrication layer comprises a solid lubricant.
 13. The piston of claim 11, wherein the lubrication layer comprises a grease, and the grease has a viscosity sufficient to adhere the grease to the interior surface of the first shoe pocket.
 14. The piston of claim 11, wherein the interior surface of the second shoe pocket comprises the lubrication layer formed thereon.
 15. A method for manufacturing a piston comprising a head portion and an engaging portion, the method comprising the steps of: forming a first shoe pocket and a second shoe pocket within the engaging portion forming a hollow portion within an interior surface of the first shoe pocket; and coating the interior surface of the first shoe pocket with a lubricant.
 16. The method of claim 15, further comprising the step of forming the hollow portion within an interior surface of the second shoe pocket.
 17. The method of claim 15, further comprising the step of forming a penetrating aperture within an interior surface of the second shoe pocket.
 18. The method of claim 15, wherein the hollow portion is formed by forging.
 19. The method of claim 15, wherein the hollow portion is formed by cutting.
 20. The method of claim 17, wherein each of the hollow portion and the penetrating aperture are formed by drilling.
 21. The method of claim 15, wherein the lubricant is selected from the group consisting of a solid lubricant and a liquid lubricant. 